Diagnostic errors remain the 
leading reason - or excuse - for medical malpractice lawsuits by the swarms of hungry sharks which parasitize American's fine physicians - the best physicians in the world. Kevin, MD.
All the more reason for docs to be irrational - or rationally irrational - in spending your money (either yours directly, or the insurance company's money - which was your money).
If you have a headache, I am going to order an MRI of your head which will cost you between $700-1100 in my area. I know darn well that you don't have a tumor, but I could be wrong 0.3% of the time. So I'll order the MRI, because you will want me to, and my law suit defensiveness will want me to. Still, I will know that it is poor medicine.
Indeed, I know that your particular pattern of headache, and your exam shows it to be a Common Migraine, and not a tumor, not an aneurysm, not a stroke or subdural, etc. And I know that all sorts of guidelines have been constructed, such as these. Well, you can toss the guidelines for all I care.
The Barrister's recent series on error
(Part 1 - Fun with the Null Hypothesis,
Part 2 - False Positives and False Negatives,
Part 3 - Risk of Inaction and Opportunity Cost)
applies beautifully to modern medicine. There is almost no end to the amount of your money we can spend to try to reduce our False Negative rates - our Type 2 errors. And they will occur, regardless.
It is very unpleasant to be sued. It damages a doctor's enjoyment of his art, it absorbs huge amounts of time and energy, and it damages his relationships with all of his patients. And, finally, it has nothing to do with his competence and everything to do with the greed and litigiousness of his patient.
I pay 42,000/year for malpractice insurance as a GP, and I have never been sued. I know guys who pay 160,000. You are paying those bills.
